This relates generally to electronic devices, and more particularly, to electronic devices with displays.
Electronic devices often include displays. For example, cellular telephones and portable computers may have displays for presenting information to a user.
Liquid crystal displays contain a layer of liquid crystal material. Display pixels in a liquid crystal display contain thin-film transistors and electrodes for applying electric fields to the liquid crystal material. The strength of the electric field in a display pixel controls the polarization state of the liquid crystal material and thereby adjusts the brightness of the display pixel.
Substrate layers such as color filter layers and thin-film transistor layers are used in liquid crystal displays. A thin-film transistor layer contains an array of the thin-film transistors that are used in controlling electric fields in the liquid crystal layer. A color filter layer contains an array of color filter elements such as red, blue, and green elements. The color filter layer provides the display with the ability to display color images. In some displays the color filter elements are formed on the thin-film transistor layer.
A backlight unit is used to provide illumination for the display. The backlight unit includes light-emitting diodes that supply light to the edge of a light guide plate. The light guide plate laterally distributes light from the light-emitting diodes across the display. Scattering features in the light guide plate cause the light in the light guide plate to scatter outwardly through the layers of the display.
In color displays, the backlight illumination is white light that includes red, green, and blue components. In some displays, the light-emitting diodes that are used to provide light to the edge of the light-guide plate emit blue light. A quantum dot enhancement film is provided in the backlight to convert some of the blue light into red and green light.
Backlight units that include blue light-emitting diodes and quantum dot enhancement film can be subject to undesired blue edge effects where the peripheral edge of the backlight produces more blue light than red and green light. A display that is illuminated with this type of backlight unit will have an undesired blue color cast along its edges. The blue color cast can adversely affect the quality of images displayed on a display.
It would therefore be desirable to be able to provide improved backlights for displays such as liquid crystal displays.